In the United States, between 10 and 100 billion kilowatt-hours of electric power are used every year to light roads, highways, and parking lots at night. Airline passengers descending into a city on a clear night can easily see the extent to which electricity is being used to light streets and roads throughout the night for the purpose of safety and security. Much of the time, this energy is being expended unnecessarily when thoroughfares are untraveled and parking lots are vacant. Not only is the United States wasting a tremendous amount of electrical energy by perpetually illuminating empty streets and parking lots, but extraneous lights also cause “light noise,” a form of light pollution that has become so extreme that few city dwellers ever see stars, even on a cloudless night. Furthermore, by-products created by this wasted energy may continue to have a lasting and destructive impact on the environment.
Despite the wasted energy, parking lot security remains insufficient, and nighttime crime continues to pose a serious problem at colleges, in commercial areas, and in public spaces. More than 60% of crime on university campuses is reported to take place in parking lots. Parking lots are often considered the most dangerous locations for business commuters and apartment dwellers (“Campus Communications” and “Parking Protection,” by John Mesenbrink, Security Magazine, September 2001). Malls and shopping centers also lack nighttime parking lot security, and the most dangerous incidents occurring in public parks take place at night.
Lights and cameras are typical devices deployed to improve security. Until the present time, society has paid for security with a high electric bill resulting from keeping fixtures illuminated continuously. A second security precaution, video surveillance cameras, is added to act as a deterrent, but most cameras record for later review only events that have already occurred. Fewer than 5% of surveillance cameras are monitored; therefore, they do not proactively prevent crime.
Indoor incandescent lights currently use occupancy sensors or motion detectors to automatically activate switching and thereby save energy. Unfortunately, these systems are ineffective in large, open outdoor areas. They work well indoors because incandescent lamps used to light interior spaces are capable of switching on and off quickly. Some fast-start fluorescent lights also switch sufficiently fast for indoor applications. However, gymnasium lighting or lights used in large, open retail stores over long periods of time generally use gas vapor lighting to save energy. Unfortunately, gas vapor bulbs cannot be switched on or off quickly, and they are difficult to dim effectively. Because they are too slow to switch on and off in response to real-time activity, these existing fixtures are incompatible with motion or occupancy sensors.
Most outdoor lighting for streets and parking lots also uses sodium vapor or other gas vapor bulbs. These light sources are chosen for maximum efficiency because they require the least amount of energy. Typical sodium vapor lamps used in street lights have efficiencies of about 100-150 lumens per Watt. Low pressure sodium vapor lamps may reach even higher efficiencies, up to 200 lumens per Watt, but they are seldom used because of the strong yellow cast characterizing their light output, rather than the preferred white light. For this reason, some large area lighting applications, especially in locations like retail stores, have switched to metal halide lamps, because of their truer white light output. However, metal halide efficiencies are not so high, only about 80-125 lumens per Watt, and they have shorter lifetimes, which are the reasons why metal halide lamps are not used so often for street lights. Moreover, the above-mentioned efficiencies of metal halide lamps and sodium vapor lamps are primarily achieved after the lamps are heated. When gas vapor lamps are cold, efficiencies and light output are much lower, and ballasts required for these gas vapor lamps reduce efficiencies even further.
Motion sensors controlling indoor incandescent or special fluorescent lights typically employ either infrared or ultrasonic technology. The most common indoor motion sensor is a low cost far-infrared detector, which is ideal for detecting human beings traversing a room. Infrared detectors are also used in incandescent “security lights” near entryways or exits; however, when used outdoors, infrared detectors commonly exhibit false triggering, as many security companies have discovered. Furthermore, the detection range of infrared detectors is limited, and the detectors lose sensitivity as outdoor temperatures increase. Other indoor occupancy sensors rely on ultrasonic detectors. An ultrasonic detector transmits into a closed room sound waves at frequencies beyond the range of human hearing. The detector then detects a shift in frequency by sensing reflected waves and comparing the transmitted and reflected frequencies. An object in the path of the sound wave moving in a direction toward or away from the sensor compresses the wave, thereby perturbing the frequency and introducing a “Doppler” shift. While they are very sensitive to small changes within a closed room, like infrared motion sensors, ultrasonic sensors do not recognize a target if it stops moving. Being highly sensitive, ultrasonic sensors are subject to false triggering by outdoor wind and air turbulence. Furthermore, because they depend on reflections, ultrasonic sensors are unsuitable for use in wide open or partly enclosed spaces, effectively restricting them to indoor environments.
Intelligent sensors for use outdoors in traffic control applications are generally unable to recognize moving vehicles or pedestrians along a long stretch of road. The intelligent sensors cannot distinguish human or vehicular motion from that of animals, newspapers blowing in the wind, parked cars, or a variety of other distractions. Even the most sophisticated outdoor motion sensors, which are much more expensive than the indoor variety, may not distinguish between animals and human beings. Intelligent sensors may not detect moving vehicles sufficiently far away to turn on street lights soon enough, unless the vehicles are moving very slowly. When cars are cold, for instance, upon ignition, infrared sensors have difficulty detecting cars located far away, because the sensors respond primarily to spatial temperature changes.
U.S. Pat. Nos. 7,045,968 and 6,909,921 describe indoor incandescent lighting control systems, including the use of motion sensors, in the latter case. U.S. Pat. No. 6,151,529 describes an intelligent lighting control system for indoor lights based upon analysis of data from simple motion sensors. U.S. Pat. No. 6,114,816 describes a lighting system that controls gas discharge lamps, dimming them automatically according to slow changes sensed in the immediate environment such as time of day and ambient light level. Occupancy levels are mentioned, but primarily in reference to slowly changing occupancy. U.S. Pat. No. 5,986,357 features an occupancy sensor utilizing ultrasonic and infrared sensors, combined for use in indoor lighting control. U.S. Patent Application Pub. No. 2005/0281030 for “Lighting Control Using LED Lighting with Fluorescent Lighting Fixtures” focuses on indoor applications and does not mention image or video sensors. What is needed, therefore, is a system for and method of preventing energy waste by intelligently controlling activation and brightness of outdoor lighting so that lights remain on only when they are useful, while simultaneously improving security in parking lots and outdoor public spaces.